PROJECT SUMMARY Childhood caries is a serious public health problem affecting the immediate and long-term quality of life of both the child and its family. Recent studies have shown an increased prevalence of caries in HIV-infected children. Furthermore, HIV-infected children on highly active antiretroviral therapy (HAART) show decreased salivary flow rates, which likely predispose them to caries. These findings reinforce the need for evidence based prevention and treatment for the promotion and maintenance of oral health. It is now well documented that the human microbiome is intimately associated with our health, and studies focusing on the gut microbiome have shown adverse community shifts for HIV+ individuals, where normal commensals are depleted and pathogens enriched. Preliminary studies of the impact of HIV infection on the oral microbiome have shown that the distribution of certain species of bacteria and fungus in saliva is different between healthy and HIV+ individuals. Dental plaque communities show a dramatic shift in taxonomic composition as a tooth transitions from health to disease that includes a decrease in potentially beneficial bacteria that produce basic compounds and an increase in highly acidogenic and aciduric taxa. The objective of this project is to provide a detailed taxonomic and gene expression characterization of dental plaque communities at different stages of caries for children subject to HIV exposure, infection, and treatment. To accomplish this, we will take advantage of a unique cohort of HIV infected children in Nigeria. Here, we will take an innovative approach that (i) combines the 16S rRNA gene with two additional loci that provide species level resolution for the Streptococci, Neisseria, and fungi, and (ii) incorporates detailed taxonomic profiling in the construction of a reference pan-genome for metatranscriptomics. In Aim 1, for HIV-infected children on HAART, HIV exposed but uninfected children, and unexposed and uninfected (HUU) children, we will utilize metagenomics (high throughput amplicon sequencing) to profile the taxonomic composition of plaque samples obtained from teeth that represent six progressive stages of caries. In Aim 2, using plaque samples obtained from teeth that represent six progressive stages of caries, obtained from HIV-infected children on HAART and unexposed/uninfected children we will utilize metatranscriptomics to measure changes in community gene expression to determine how bacteria and fungal metabolic pathways involved in caries are influenced by HIV infection and treatment. We anticipate that these aims will yield the first detailed insight into how HIV exposure, infection, and treatment affect the ecology and development of caries in children. Ultimately, this knowledge will translate into improved prevention and intervention stratergies that could potentially mitigate an increased risk of caries in an HIV infected child.